Device for generating an atmospheric-pressure plasma

ABSTRACT

A device for generating an atmospheric-pressure plasma is disclosed. In an embodiment the device includes a piezoelectric transformer comprising an input region and an output region, wherein the input region is designed to convert an applied alternating voltage into a mechanical oscillation, wherein the output region is designed to convert a mechanical oscillation into a voltage, and wherein the output region adjoins the input region in a longitudinal direction, a contact element fastened to the piezoelectric transformer, the contact element being designed to apply the alternating voltage to the input region and a holder, wherein the contact element is connected to the holder by a form-fit connection, in such a manner that a movement of the piezoelectric transformer in the longitudinal direction, relative to the holder, is prevented.

This patent application is a national phase filing under section 371 ofPCT/EP2017/052615, filed Feb. 7, 2017, which claims the priority ofGerman patent application 10 2016 102 585.2, filed Feb. 15, 2016, eachof which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a device for generating anatmospheric-pressure plasma. The plasma in this case is a non-thermalplasma.

SUMMARY OF THE INVENTION

Embodiments provide a device that has a piezoelectric transformer, whichgenerates an output voltage that can be used for ionization of a processgas. Further embodiments provide a device that should avoid movements ofthe piezoelectric transformer, in particular in the longitudinaldirection, relative to a holder of the device. At the same time,however, the holder should not adversely affect the piezoelectrictransformer in such a manner that oscillations of the transformer aredamped, since the efficiency of the plasma generation would be reducedas a result.

Embodiments provide a device that as fully as possible fulfils theseinitially contradictory requirements.

Embodiments provide a device for generating an atmospheric-pressureplasma, which has a piezoelectric transformer, a contact element and aholder. The piezoelectric transformer has an input region and an outputregion, wherein the input region is designed to convert an appliedalternating voltage into a mechanical oscillation, wherein the outputregion is designed to convert a mechanical oscillation into a voltage,and wherein the output region adjoins the input region in a longitudinaldirection. The contact element is fastened to the piezoelectrictransformer and is designed to apply an alternating voltage to the inputregion. In addition, the contact element is connected to the holder by aform-fit connection, in such a manner that a movement of thepiezoelectric transformer in the longitudinal direction, relative to theholder, is prevented.

A connection of at least two connection partners that is produced as aresult of the at least two connection partners engaging in one anothermay be referred to as a “form-fit connection.” The connection partnersin this case cannot separate from each other, even if there is notransmission of force, or if transmission of force is interrupted. Inother words, in the case of a form-fit connection, a movement of oneconnection partner is blocked in at least one direction by the otherconnection partner. In the case of operating load, pressure forces actnormally, i.e., at right angles, to the surfaces of the connectionpartners. In the present case, the contact element and the holder formthe connection partners of the form-fit connection, a movement of thecontact element in the longitudinal direction being blocked by the shapeof the holder.

A movement of the piezoelectric transformer in the longitudinaldirection is not prevented as a result of the holder being directlyconnected to the piezoelectric transformer, but as a result of theholder being connected to the contact element, which in turn is fastenedto the transformer. A device is thereby created in which the mechanicalfastening of the contact element to the piezoelectric transformer issubjected only to slight mechanical loads. Thus, for example, theservice life of solder points, at which the contact element is solderedto the outer electrodes, is prolonged considerably.

Moreover, the holder thus does not damp the oscillations of thepiezoelectric transformer in the longitudinal direction, since theholder does not act directly upon the piezoelectric transformer.Accordingly, plasma can be produced in a highly efficient manner.

The form-fit connection may be, in particular, impact resistant, suchthat, for example, even dropping of the device would not result in alongitudinal movement of the piezoelectric transformer relative to theholder.

The holder can thus serve several purposes simultaneously. Owing to itsform-fit connection to the contact element, it can fix the piezoelectrictransformer in its longitudinal position. At the same time, it isconstructed such that the vibrations of the piezoelectric transformerare not damped, or at least are only minimally damped, since the fixingby means of the form-fit to the contact element does not significantlyadversely affect these vibrations of the transformer. In addition, theholder can also serve to mechanically protect the transformer, forexample, against impacts.

The holder may have two projections, wherein on both sides the contactelement bears directly against respectively one of the two projectionsin the longitudinal direction. Accordingly, the contact element can beenclosed in a form-fitting manner between the two projections.

Alternatively or in addition, the holder may have slot-type recesses inwhich the contact element is arranged, and through which the contactelement is run out from the holder, from an interior of the holder. Aform-fit connection between the contact element and the holder may alsobe created by arranging the contact elements in the slot-type recessesof the holder. The slot-type recesses may extend in the longitudinaldirection. In the spatial directions perpendicular to the longitudinaldirection, the slot-type recesses may have a significantly lesser extentthan in the longitudinal direction.

Alternatively or additionally, the contact element may have two wires,wherein the holder has openings, the diameter of which corresponds to adiameter of the wires, wherein each of the two wires goes throughrespectively two openings in the holder and is thereby connected to theholder in a form-fitting manner. The diameter of the openings may, inparticular, be slightly greater than the diameter of the wires, suchthat a form-fit is obtained when a wire is arranged in the opening.

The contact element may be fastened to the piezoelectric transformer bya non-separable fastening. A non-separable fastening in this case mayrefer to all fastenings that cannot be separated without therebydestroying, or at least damaging, at least one of the elements that arefastened together.

Such a non-separable fastening of the contact element to thepiezoelectric transformer may be produced, for example, by soldering,bonding, adhesive bonding, or microsilver sintering. In the case ofmicrosilver sintering, a paste is applied between the contact elementand the transformer, and the contact element and the transformer arethen sintered to each other. Formed from the paste in the sinteringprocess is a layer that is composed of at least 95 weight % silver andthat mechanically connects the contact element and the piezoelectrictransformer to each other.

The holder may have at least two support elements, on which thepiezoelectric transformer is supported and which prevent a movement ofthe piezoelectric transformer in a direction perpendicular to thelongitudinal direction. Movements in this case are movements of thepiezoelectric transformer relative to the holder.

In particular, the holder may have a first pair consisting of twosupport elements, and a second pair consisting of two support elements,the first pair preventing a movement of the transformer, relative to theholder, in a first direction perpendicular to the longitudinaldirection, and the second pair preventing a movement of the transformer,relative to the holder, in a second direction that is perpendicular tothe longitudinal direction and perpendicular to the first direction.

The support elements can accordingly prevent movements of thepiezoelectric transformer in directions perpendicular to thelongitudinal direction, without the fastenings of the contact element tothe piezoelectric transformer, for example, the solder points, beingthereby mechanically loaded. Such movements perpendicular to thelongitudinal direction may be triggered, for example, as a result ofimpacts.

The transformer may be supported on the support elements, such that thesupport elements do not exert a permanent clamping effect upon thetransformer, but only exert a force upon the transformer if the latterwould otherwise move, relative to the holder, perpendicularly inrelation to the longitudinal direction. As a result of being supportedon the support elements, the transformer can thus be prevented frommoving in a direction perpendicular to the longitudinal direction. Sincethe support elements do not exert a permanent force upon thetransformer, it can be ensured that the support elements do not damp anoscillation of the transformer in the longitudinal direction.

The support elements may be of a shape that tapers in the form of awedge toward the piezoelectric transformer and bear against thepiezoelectric transformer in a virtually linear manner. Accordingly, thesupport elements bear with only a minimal surface area against thepiezoelectric transformer. In this way, damping of the oscillation ofthe transformer by the support elements can be reduced yet further.

The support elements may be arranged in such a manner that they bearagainst the piezoelectric transformer, in the longitudinal direction, ata position that corresponds to one quarter or three quarters of thelength of the piezoelectric transformer. At these positions, oscillationnodes can be realized when the piezoelectric transformer is operated atits resonant frequency, or with a harmonic component of the resonantfrequency. Accordingly, during operation of the device, thepiezoelectric transformer moves only minimally at these position. Thearrangement of the support elements at these positions can also beinstrumental in the support elements not significantly damping theoscillations of the piezoelectric transformer.

The holder may be composed of a material that deforms predominantlyelastically. Owing to the predominant elastic deformation, a highquality factor, in particular, can be obtained. In particular, thematerial may be a hard material. In particular, the support elements maybe composed of a material that deforms predominantly elastically. Aholder made of rubber or other plastically deforming material wouldresult in damping of the oscillation of the piezoelectric transformer.By use of a material that deforms predominantly elastically, it can beensured that the oscillations of the transformer cannot be mechanicallytransmitted to the holder and, accordingly, are not damped.

The material may be, for example, polybutylene terephthalate (PBT),polytetrafluorethylene (PTFE), or a polyamide, which may additionallyhave glass fiber components.

The holder may have two half-shells that are connected to each other. Afastening of the piezoelectric transformer, or of the contact elements,may be produced in this case by the connection of the two half-shells.

The two half-shells may be identical to one another. Further, the twohalf-shells may be made from one material. In particular, the twohalf-shells may have been fabricated by means of injection molding froman injection molding compound, and one and the same mould may be used tofabricate both half-shells. The use of a holder consisting of twoidentical half-shells can thus render possible a simple productionmethod in which it is necessary to use only one single injection mould.

The contact element may have a metal plate that comprisescopper-invar-copper (CIC=Copper-Invar-Copper). Copper-invar-copper hasthe advantage of a very low coefficient of thermal expansion. Moreover,a metal plate comprising copper-invar-copper can be pressed intodiffering shapes, and accordingly allows a high degree of designflexibility in the design of the contacting of the device.

The metal plate may have a first portion, which bears against thepiezoelectric transformer, and a second portion, which is arranged on anexterior of the holder. For this purpose, the metal plate may be bent.For example, the metal plate may be bent in a U shape. Alternatively,the metal plate may be bent in such a manner that it has right-angledbends that separate the portions from each other.

In addition, the holder may have a guide element, the shape of whichmatches the shape of the metal plate. For example, the plate and theguide element may each have a semicircular portion. The metal plate andthe holder may be arranged in such a manner that a form-fit connectionof the metal plate and the holder is produced.

The metal plate may additionally have a middle portion, which connectsthe first portion to the second portion, wherein the metal plate is bentin a U shape. In particular, the middle portion may realize thesemicircular portion of the U shape. The first and the second portionmay each form straight limbs of the U shape.

The second portion may have a bent sub-portion, which is connected tothe holder in a form-fitting manner. This form-fit connection may beadditionally instrumental in precluding relative movements between themetal plate and the holder.

The device may additionally have a web that bears against an input-sideend face of the piezoelectric transformer and thereby prevents amovement of the piezoelectric transformer in the longitudinal directiontoward the web. For example, together with the metal plate the web mayrealize a form-fit connection between the holder, the contact elementand the transformer.

A further aspect of the present invention relates to a plasma generator,having the device described above, and having a housing, in which thedevice is arranged. The plasma generator may render possible, inparticular, the generation of a non-thermal atmospheric-pressure plasma.The plasma generator may have further structural elements, besides thedevice and the housing. These include, for example, a trigger circuit, anozzle, via which the plasma can emerge, and an inlet for the processgas.

The housing may be an outer housing of the plasma generator. The holderof the device may be arranged inside the housing. Accordingly, theholder can then only be accessed when the housing is open.

The device may preferably be separably fastened in the housing, suchthat the device can be removed from the housing. In particular, thedevice has the elements of the plasma generator that particularlyfrequently exhibit signs of wear. This applies in particular to thepiezoelectric transformer, which during operation continuously executesmechanical oscillations, by which it can be damaged in the case oflong-term operation. Also in the case of long-term operation of thepiezoelectric transformer, damage may be caused by the plasma ignitionson the output side.

In particular, the plasma generator may be designed in such a mannerthat the piezoelectric transformer can only be removed together with theholder and the contact element from the plasma generator. In this case,the piezoelectric transformer, the holder and the contact element can beremoved as a unit from the plasma generator, and replaced. This makes itpossible to create a device that has the above-mentioned advantages suchas, for example, impact-resistant mounting of the transformer, onlyminimal damping of the oscillations of the transformer, or longitudinalfixing without loading of the mechanical fastening of the contactelements to the transformer.

If the device is designed in such a manner that it can be taken out ofthe plasma generator and replaced, then, following replacement of thedevice, the other structural elements of the plasma generator cancontinue to be used.

The holder of the device may be fastened in the housing of the plasmagenerator, for example, by a screwed connection or a latchingconnection. The connection may be designed in such a manner that it doesnot separate as a result of impacts and vibrations during operation ofthe plasma generator, but cannot be separated by a user of the plasmagenerator.

The device may alternatively be fastened in the housing by a materialconnection, for example, by adhesive bonding or soldering. Although sucha connection cannot be separated, it can nevertheless be advantageous inthe case of particular applications that require a particularly highlevel of fastening stability.

A control circuit, for controlling the piezoelectric transformer, whichis electrically contacted to the piezoelectric transformer via thecontact element, may be arranged in the housing. If the holder isfastened in the housing, then in this case an electrical contact can berealized between the contact element and the control circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described further in the following on the basisof the figures.

FIG. 1 shows a piezoelectric transformer in a perspective view;

FIG. 2 shows a device or generating an atmospheric-pressure plasma;

FIG. 3 shows a detail of a cross section through the device shown inFIG. 2;

FIG. 4 shows a perspective view of the device;

FIGS. 5 to 10 show a cross section through a device according toalternative exemplary embodiments;

FIG. 11 shows a side view of a piezoelectric transformer and a contactelement;

FIGS. 12 to 15 show the device for generating an atmospheric-pressureplasma according to a further exemplary embodiment;

FIGS. 16 to 19 show the device according to a further exemplaryembodiment;

FIG. 20 shows a cross section through the device according to analternative variant of the exemplary embodiment shown in FIGS. 16 to 19;

FIG. 21 shows a cross section through the device according to a furtherexemplary embodiment; and

FIG. 22 shows an alternative variant of the exemplary embodiment shownin FIG. 21.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 shows a piezoelectric transformer 1 in a perspective view. Thepiezoelectric transformer 1 may be used, in particular, in a device forgenerating non-thermal atmospheric-pressure plasma.

A piezoelectric transformer 1 is a type of resonant transformer that isbased on piezo-electricity and that, unlike the conventional magnetictransformers, constitutes an electromechanical system. The piezoelectrictransformer 1 is, for example, a Rosen-type transformer.

The piezoelectric transformer 1 has an input region 2 and an outputregion 3, the output region 3 adjoining the input region 2 in alongitudinal direction z. In the input region 2 the piezoelectrictransformer 1 has electrodes 4, to which an alternating voltage can beapplied. The electrodes 4 extend in the longitudinal direction z of thepiezoelectric transformer 1. The electrodes 4 are stacked, alternatingwith a piezoelectric material 5, in a stacking direction x, which isperpendicular to the longitudinal direction z. The piezoelectricmaterial 5 in this case is polarized in the stacking direction x.

The electrodes 4 are arranged inside the piezoelectric transformer 1,and are also referred to as internal electrodes. The piezoelectrictransformer 1 has a first lateral face 6, and a second lateral face 7that is opposite the first lateral face 6. A first external electrode 8is arranged on the first lateral face 6. A second external electrode(not shown) is arranged on the second lateral face 7. The internalelectrodes 4 are electrically contacted in an alternating manner in thestacking direction x, either to the first external electrode 8 or to thesecond external electrode.

The piezoelectric transformer 1 additionally has a third lateral face 20and a fourth lateral face 21, which are opposite each other and whichare arranged perpendicularly in relation to the first lateral face 6 andthe second lateral face 7. The surface normals of the third and fourthlateral faces 20, 21 each run in the stacking direction x.

The input region 2 can be controlled with a small alternating voltage,which is applied between the electrodes 4. Owing to the piezoelectriceffect, the alternating voltage applied on the input side in firstconverted into a mechanical oscillation. The frequency of the mechanicaloscillation in this case depends substantially on the geometry and themechanical structure of the piezoelectric transformer 1.

The output region 3 comprises piezoelectric material 9, and does nothave internal electrodes. The piezoelectric material 9 in the outputregion is polarized in the longitudinal direction z. The piezoelectricmaterial 9 of the output region 3 may be the same material as thepiezoelectric material 5 of the input region 2, and the piezoelectricmaterials 5 and 9 may differ in their direction of polarization. In theoutput region 3, the piezoelectric material 9 is shaped to form asingle, monolithic layer, which is polarized entirely in thelongitudinal direction z. In this case, the piezoelectric material 9 inthe output region 3 has only a single direction of polarization.

If there is an alternating voltage applied to the electrodes 4 in theinput region 2, a mechanical wave, which generates an output voltage inthe output region 3 as a result of the piezoelectric effect, is realizedwithin the piezoelectric material 5, 9. The output region 3 has anoutput-side end face 10. Thus, in the output region 3, a voltage isgenerated between the end face 10 and the end of the electrodes of theinput region 2. A high voltage is generated in this case at theoutput-side end face 10. Also produced in this case, between theoutput-side end face and an area around the piezoelectric transformer,is a high potential difference that is sufficient to generate a strongelectric field, which ionizes a process gas.

In this way, the piezoelectric transformer 1 generates strong electricfields that are capable of ionizing gases or liquids by electricalexcitation. In this case, atoms or molecules of the respective gas or ofthe respective liquid are ionized, and form a plasma. Ionization occurswhenever the electrical field strength at the surface of thepiezoelectric transformer 1 exceeds the ignition field strength of theplasma. Ignition field strength of a plasma refers to the field strengththat is required to ionize the atoms or molecules.

FIG. 2 shows a device 11 for generating an atmospheric-pressure plasma.The device 11 comprises the piezoelectric transformer 1 shown in FIG. 1.Here, the piezoelectric transformer 1 additionally has an insulation 12,which is arranged in the output region 3 of the piezoelectrictransformer 1, the insulation 12 at least partially covering the lateralfaces of the transformer 1 in the output region 3, and the output-sideend face 10 being without insulation 12. The insulation may be formed,for example, by a shrink-on sleeve. The insulation 12 prevents unwantedplasma ignitions from occurring along the output-side edges of thepiezoelectric transformer 1.

The device additionally has a first contact element 13 and a secondcontact element 14. The first contact element 13 is connected to thefirst external electrode 8 of the piezoelectric transformer 1. Thesecond contact element 14 is connected to the second external electrodeof the piezoelectric transformer 1. Via the first and the second contactelement 13, 14, an alternating voltage can be applied to the first andthe second external electrode of the piezoelectric transformer 1.

The contact elements 13, 14 each have a wire 15, arranged at the end ofwhich there is a block 16. The block 16 of the contact elements 13, 14is fastened to the respective external electrode 8 by a non-separablefastening. For example, the block 16 may be fastened to the externalelectrode 8 of the piezoelectric transformer 1 by soldering, bonding,adhesive-bonding or microsilver sintering. The block 16 and the wire 15comprise a conductive material, for example, copper.

The device 11 additionally has a holder 17. The holder 17 may have twohalf-shells 18, 19. In FIG. 2, only one first half-shell 18 of theholder 17 is shown, to enable the connection of the piezoelectrictransformer 1 to the holder 17 to be shown. The second half-shell 19 maybe identical to the half-shell 18 shown in FIG. 2. The half-shells 18,19 have injection-molded elements.

The holder 17 has support elements 22. The third and the fourth lateralface 20, 21 of the piezoelectric transformer 1 each bear against one ofthe support elements 22. The support elements 22 are each tapered in theform of a wedge toward the piezoelectric transformer 1, such that theybear in a virtually linear manner against the piezoelectric transformer1. The support elements 22 in this case are arranged, along thelongitudinal direction z, at the positions at which oscillation nodesare realized when the piezoelectric transformer 1 is operated at itsresonant frequency, or with a harmonic components. Accordingly, thesupport elements 22 are arranged at a length of one quarter of thelength of the piezoelectric transformer 1 and at three quarters of thelength of the piezoelectric transformer 1.

Owing to the arrangement of the support elements 22 at the oscillationnodes of the piezoelectric transformer 1, and owing to theirwedge-shaped design, the effect is achieved that the support elements 22only minimally damp a movement of the piezoelectric transformer 1 in thelongitudinal direction.

In the stacking direction x, on both sides the piezoelectric transformer1 bears directly against respectively one of the two support elements22. The support elements 22 are opposite one another in the stackingdirection x. In this way, movements of the piezoelectric transformer 1,relative to the holder 17, in the stacking direction x are prevented.

The holder 17 additionally has further support elements 23, betweenwhich the piezoelectric transformer 1 is enclosed in a y direction, they direction being perpendicular to the stacking direction x andperpendicular to the longitudinal direction z. In the y direction, thepiezoelectric transformer 1 can bear directly against a respectivesupport element 23. The support elements 23 are opposite one another inthe y direction. These support elements 23 likewise taper in the form ofa wedge toward the piezoelectric transformer 1, and bear against thelatter in a virtually linear manner. As a result of bearing against thesupport elements 23, a movement of the piezoelectric transformer 1,relative to the holder 17, in the y direction is prevented.

FIG. 3 shows a detail of a cross section through the device 11 forgenerating an atmospheric-pressure plasma. FIG. 3 shows the firsthalf-shell 18 and the second half-shell 19 of the holder 17. It can beseen that each of the half-shells 18, 19 has projections 24, the block16 of the contact element 13, 14 being arranged, in the longitudinaldirection z, between two projections 24. In the longitudinal directionz, the contact elements 13, 14 in this case each bear against both afirst projection 24 and a second projection 24. Accordingly, a movementof the contact elements 13, 14 in the longitudinal direction z, relativeto the holder 17, is prevented. A form-fit connection of the contactelements 13, 14 to the holder 17 is realized. Since the contact elementsare fixedly connected to the respective external electrode 8 of thepiezoelectric transformer 1, a movement of the piezoelectric transformer1 in the longitudinal direction z, relative to the holder 17, is alsonot possible.

During operation, the piezoelectric transformer 1 executes oscillationsin the longitudinal direction z. Owing to the form-fit connection of thecontact elements 13, 14 to the holder 17, it is ensured that thetransformer 1 is not moved relative to the holder 17 by thisoscillation. The form-fit connection is additionally impact-resistant,such that the piezoelectric transformer 1 is not moved relative to theholder 17 even if the device 11 is subjected to an impact, for example,as a result of being dropped.

Owing to the wedge shape of the support elements 22, 23, movements ofthe piezoelectric transformer 1, relative to the holder 17, indirections x, y perpendicular to the longitudinal direction z areavoided, without mechanical loading of the fastening of the contactelements 13, 14 to the piezoelectric transformer 1. This fastening maybe, for example, solder points. Instead, mechanical loading occurs atthe points of connection of the contact elements 13, 14 to the holder17. It is thereby ensured that the piezoelectric transformer 1 itself isnot destroyed by the mechanical loads, and that the electricalcontacting of the piezoelectric transformer 1 is not disturbed.

The two half-shells 18, 19 of the holder 18 may be identical. The twohalf-shells 18, 19 are additionally fastened to each other in such amanner that they cannot be non-destructively separated from each other.For example, the two half-shells 18, 19 may be adhesive-bonded to eachother.

FIG. 4 shows a perspective view of the device 11. The output region 3 ofthe piezoelectric transformer 1 can be seen in FIG. 4. Also shown inFIG. 4 are the support elements 22, 23, which are arranged at alongitudinal length of three quarters of the piezoelectric transformer1. Two support elements 22 prevent a movement of the piezoelectrictransformer 1, relative to the holder 17, in the stacking direction x,and two support elements 23 prevent a movement of the piezoelectrictransformer 1, relative to the holder 17, in the y direction.

The device 11 may be used, in particular, in a plasma generator. Theholder 17 in this case may be fastened in a housing of the plasmagenerator. The device 11 is designed in such a manner that the device 11can be taken back out of the plasma generator, and can be replaced byanother device 11 of the same type. Accordingly, the device 11 can beseparably fastened in the housing of the generator, for example, bymeans of a screwed connection or a latching connection.

The plasma generator has further elements besides the device 11, forexample, a control circuit. The piezoelectric transformer 1 may beelectrically contacted to the control circuit via the contact elements13, 14. The control circuit in this case may apply an alternatingvoltage to the input region 2 of the piezoelectric transformer 1 via thecontact elements 13, 14.

In a plasma generator, the piezoelectric transformer 1 in particular isa component part that may exhibit signs of wear and that, accordingly,should advantageously be replaceable. The device 11 enables thepiezoelectric transformer 1 to be replaced in the plasma generator,together with the holder 17 and the contact elements 13, 14, without thenecessity of also replacing further structural elements of the plasmagenerator. At the same time, the device 11 allows the piezoelectrictransformer 1 to be held in a defined position without significantlyimpairing it in its operation, in particular without substantiallydamping the oscillations of the piezoelectric transformer 1.

FIGS. 5 to 10 show a cross section through a device 11 according toalternative exemplary embodiments. The contact elements 13, 14 in thiscase are formed by a metal plate 25 comprising copper-invar-copper. Thecontact elements 13, 14 are fixedly fastened to the external electrodesof the piezoelectric transformer 1, for example, by soldering, bonding,adhesive bonding or microsilver sintering.

The holder 17 has slot-type recesses 26. The contact elements 13, 14 arearranged in the recesses 26. The contact elements 13, 14 are run outfrom the interior of the holder 17 into the exterior of the holder 17through the recesses 26. The contact elements 13, 14 are fastened in aform-fit manner in the recesses 26. Movements of the contact elements13, 14, relative to the holder 17, in the longitudinal direction x arethereby avoided. In addition, the contact elements 13, 14 may beadhesive-bonded to the holder 17 at the recesses 26, in order to achievea more stable fastening.

FIGS. 5 to 10 show differing shapes of the contact elements 13, 14. Thecontact elements 13, 14 in this case are each fastened over a surfacearea to the respective external electrode 8 of the piezoelectrictransformer 1.

FIG. 11 shows a side view of the piezoelectric transformer 1 and of acontact element 13. Here, likewise, it can be seen that the contactelement 13 is connected over a surface area to the external electrode 8of the piezoelectric transformer 1. It can thereby be ensured that thefastening of the contact element 13 to the external electrode 8 isstable.

FIGS. 12 to 15 show the device 11 according to a further exemplaryembodiment. FIG. 12 and FIG. 13 each show a perspective view of thedevice 11, but the second half-shell 19 of the holder 17 are not shown,in order that the elements arranged inside the holder 17 can berepresented. FIG. 14 shows a perspective representation of the device11, with the second half-shell 19 also being shown. FIG. 15 shows across section through the device 11 shown in FIG. 14.

Here, the contact elements 13, 14 are formed by two wires 27. The holder17 has four openings 28. There are two openings 28 arranged in the firsthalf-shell 18. Likewise, there are two openings 28 arranged in thesecond half-shell 19. Each of the two wires 27 runs through an opening28 in the first half-shell 18 and an opening 28 in the second half-shell19. The diameter of the openings 28 is matched to the diameter of thewires 27, such that the wires 27 are connected to the holder 17 in aform-fitting manner. The wires 27 have a linear course inside the holder17.

In addition, the wires 27 are soldered to the piezoelectric transformer1. In particular, one of the wires 27 is soldered to the first externalelectrode 8 of the piezoelectric transformer 1, and the other of thewires 27 is soldered to the second exterior electrode. Owing to theform-fit between the wires 27 and the holder 17, and the soldering ofthe wires 27 to the piezoelectric transformer 1, the piezoelectrictransformer 1 cannot move relative to the holder 17 in the longitudinaldirection z. Moreover, owing to the form-fit of the wires with theholder 17, and the soldering of the wires 27 to the transformer 1, amovement of the transformer 1 in the y direction, relative to the holder17, is prevented in the input region 2.

The holder 17 additionally has support elements 22, on which thepiezoelectric transformer 1 is supported, and which prevent a movementof the piezoelectric transformer 1, relative to the holder 17, in thestacking direction x, and support elements 23, which prevent a movementof the piezoelectric transformer 1 in the y direction. Two supportelements 22 are arranged in the input region 2 of the transformer 1 at alength of one quarter of the length of the piezoelectric transformer 1.The third and the fourth lateral face 20, 21 of the transformer 1 bearagainst the support elements 22. Further support elements 22, 23 arearranged in the output region 3 of the transformer 1, at a length ofthree quarters of the transformer 1. Here, the first lateral face 6, thesecond lateral face 7, the third lateral face 20 and the fourth lateralface 21 are each supported on a support element 22, 23.

In addition, the holder has projections 29 on its exterior. These servefor surface mounting of the device 11 (SMD=Surface Mounted Device). Thewires 27 that come out of the openings 28 in the first half-shell 18each have a 90° bend 30 outside the holder 17. This bent shape of thewires 27 likewise serves to enable surface mounting of the device 11.

FIGS. 16 to 19 show the device 11 according to a further exemplaryembodiment. FIGS. 16, 17 and 18 each show a perspective view of thedevice 11, but the second half-shell 19 of the holder 17 is not shown,so that the elements arranged inside the holder 17 can be shown. FIG. 19shows a cross section through the device 11 shown in FIGS. 16 to 18.

In this exemplary embodiment, the contact element 13, 14 has a metalplate 25. The metal plate 25 is composed of a copper layer, an invarlayer and a further copper layer, arranged over one another in thissequence.

The metal plate 25 is in the shape of a U. The metal plate 25 has afirst portion 31 and a second portion 32, which are connected to eachother via a middle semicircular portion 33. The first portion 31 of themetal plate 24 bears against the input region 2 of the piezoelectrictransformer 1. The first portion 31 may be fixedly connected to thepiezoelectric transformer 1, for example, by a soldered connection, abond connection, an adhesive connection or a sintered connection withmicrosilver.

The holder 17 additionally has a guide element 34, which defines thearrangement of the metal plate 25. The guide element 34 has asemicircular portion, against which there bears the middle semicircularportion 33 of the metal plate 25.

The holder 17 additionally has a continuous web 37, which prevents thetransformer 1 from moving out along the longitudinal direction z, in thedirection of the input region 2, relative to the holder 17. The web 37bears against an input-side end face of the transformer 1, theinput-side end face facing away from the output region 3 of thetransformer 1.

In addition, the second portion 32 of the metal plate 25 is arranged onthe exterior of the holder 17. In the region in which the metal plate 25is arranged, the holder 17 has an outer diameter that is slightly lessthan the outer diameter in the other regions of the holder 17.

Owing to the web 37, which prevents the transformer 1 from moving out inthe longitudinal direction, in the direction of the input region 2, andowing to the U shape of the metal plate 25, which bears against thesemicircular guide element 34 of the holder 17 and the exterior of theholder, which is additionally connected to the piezoelectric transformer1, a form-fit is produced. Movements of the piezoelectric transformer 1in the longitudinal direction z, relative to the holder 17, are therebyalso prevented.

By means of a plug connection or a screwed connection, the device 11 cannow be inserted, or screwed, into a socket, the socket having electricalcontacts that electrically contact the metal plate 25.

The holder 17 additionally has support elements 22, 23, which arearranged in the inlet region 2 at a length of one quarter of the lengthof the transformer 1, and in the outlet region 3 at a length of threequarters of the length of the transformer 1. Each of the lateral faces6, 7, 20, 21 of the transformer 1 bears respectively against one supportelement 22, 23.

FIG. 20 shows a cross section through the device 11 according to analternative variant of the exemplary embodiment shown in FIGS. 16 to 19.In the case of the alternative variant, additionally applied to theexterior of the holder 17 there is an adhesive layer 35, which bonds thesecond portion 32 of the metal plate 25 to the holder 17.

FIG. 21 shows a cross section through the device 11 according to afurther exemplary embodiment. The exemplary embodiment shown in FIG. 21differs from the exemplary embodiment shown in FIGS. 16 to 19 in thatthe second portion 32 of the metal plate 25 additionally has a bentsub-portion 36. In particular, the bent sub-portion 36 has two bends atwhich the metal plate 25 is bent by an angle of 90° in each case. Owingto the bent sub-portion 36, an additional form-fit connection isobtained between the holder 17 and the metal plate 25. The additionalform-fit connection is additionally instrumental in precluding movementsof the piezoelectric transformer 1 in the longitudinal direction z,relative to the holder 17.

FIG. 22 shows an alternative variant of the exemplary embodiment shownin FIG. 21. In the case of the alternative variant, there isadditionally applied, on the exterior of the holder 17, an adhesivelayer 35 that bonds the second portion 32 of the metal plate 25 to theholder 17. In addition, the adhesive layer 35 is also applied on theregion of the holder 17 against which there bears the bent sub-portion36.

According to a further embodiment, the embodiment variants of FIGS. 16to 19 that are shown in FIGS. 21 and 22 may also be realized with theomission of the web 37 on the input side of the holder 17.

The invention claimed is:
 1. A device for generating anatmospheric-pressure plasma, the device comprising: a piezoelectrictransformer comprising an input region and an output region, wherein theinput region is designed to convert an applied alternating voltage intoa mechanical oscillation, wherein the output region is designed toconvert a mechanical oscillation into a voltage, and wherein the outputregion adjoins the input region in a longitudinal direction; a contactelement fastened to the piezoelectric transformer, the contact elementbeing designed to apply the alternating voltage to the input region,wherein the contact element has two wires; and a holder, wherein thecontact element is connected to the holder by a form-fit connection, insuch a manner that a movement of the piezoelectric transformer in thelongitudinal direction, relative to the holder, is prevented, whereinthe holder has openings, a diameter of which corresponds to a diameterof the wires and wherein each of the two wires goes through tworespective openings in the holder and are thereby connected to theholder in a form-fitting manner.
 2. The device as claimed in claim 1,wherein the holder has two projections, and wherein, on both sides, thecontact element bears directly against respectively one of the twoprojections in the longitudinal direction.
 3. The device as claimed inclaim 1, wherein the holder has slot-type recesses in which the contactelement is arranged, and through which the contact element is run outfrom the holder, from an interior of the holder.
 4. The device asclaimed in claim 1, wherein the contact element is fastened to thepiezoelectric transformer by a non-separable fastening.
 5. The device asclaimed in claim 1, wherein the holder has at least two supportelements, on which the piezoelectric transformer is supported and whichprevent a movement of the piezoelectric transformer in a directionperpendicular to the longitudinal direction.
 6. The device as claimed inclaim 5, wherein the support elements are of a shape that tapers in theform of a wedge toward the piezoelectric transformer and bear againstthe piezoelectric transformer in a virtually linear manner.
 7. Thedevice as claimed in claim 5, wherein the support elements are arrangedin such a manner that they bear against the piezoelectric transformer,in the longitudinal direction, at a position that corresponds to onequarter of a length of the piezoelectric transformer, and/or wherein thesupport elements are arranged in such a manner that they bear againstthe piezoelectric transformer, in the longitudinal direction, at aposition that corresponds to three quarters of the length of thepiezoelectric transformer.
 8. The device as claimed in claim 1, whereinthe holder is composed of a material that deforms predominantlyelastically.
 9. The device as claimed in claim 1, wherein the holder hastwo half-shells that are connected to each other.
 10. The device asclaimed in claim 9, wherein the two half-shells are identical, andwherein the two half-shells are made from one material.
 11. A plasmagenerator comprising: a device as claimed in claim 1; and a housing inwhich the device is arranged.
 12. The plasma generator as claimed inclaim 11, wherein the device is separably fastened in the housing, suchthat the device can be removed from the housing.
 13. The plasmagenerator as claimed in claim 11, wherein the holder is fastened in thehousing by a screwed connection or a latching connection.
 14. The plasmagenerator as claimed in claim 11, wherein the device is fastened in thehousing by a material connection.
 15. The plasma generator as claimedclaim 11, wherein a trigger circuit, for triggering the piezoelectrictransformer, which is electrically contacted to the piezoelectrictransformer via the contact element, is arranged in the housing.
 16. Adevice for generating an atmospheric-pressure plasma, the devicecomprising: a piezoelectric transformer comprising an input region andan output region, wherein the input region is designed to convert anapplied alternating voltage into a mechanical oscillation, wherein theoutput region is designed to convert a mechanical oscillation into avoltage, and wherein the output region adjoins the input region in alongitudinal direction; a contact element fastened to the piezoelectrictransformer, the contact element being designed to apply the alternatingvoltage to the input region, wherein the contact element has a metalplate that comprises copper-invar-copper; and a holder, wherein thecontact element is connected to the holder by a form-fit connection, insuch a manner that a movement of the piezoelectric transformer in thelongitudinal direction, relative to the holder, is prevented.
 17. Thedevice as claimed in claim 16, wherein the metal plate has a firstportion, which bears against the piezoelectric transformer, and a secondportion, which is arranged on an exterior of the holder.
 18. The deviceas claimed in claim 17, wherein the metal plate comprises additionally amiddle portion, which connects the first portion to the second portion,and wherein the metal plate is bent in a U shape.
 19. The device asclaimed in claim 17, wherein the second portion has a bent sub-portion,which is connected to the holder in a form-fitting manner.
 20. Thedevice as claimed in claim 17, wherein the device additionally has a webthat bears against an input-side end face of the piezoelectrictransformer and thereby prevents a movement of the piezoelectrictransformer in the longitudinal direction toward the web.
 21. A devicefor generating an atmospheric-pressure plasma, the device comprising: apiezoelectric transformer comprising an input region and an outputregion, wherein the input region is designed to convert an appliedalternating voltage into a mechanical oscillation, wherein the outputregion is designed to convert a mechanical oscillation into a voltage,and wherein the output region adjoins the input region in a longitudinaldirection; a contact element fastened to the piezoelectric transformer,the contact element being designed to apply the alternating voltage tothe input region; and a holder, wherein the contact element is connectedto the holder by a form-fit connection, in such a manner that a movementof the piezoelectric transformer in the longitudinal direction, relativeto the holder, is prevented, and wherein the holder has two identicalhalf-shells that are connected to each other, the two half-shells beingmade from one material.